1. Field of the Invention
The present invention relates to a power semiconductor device, which is applicable to, for example, general-purpose inverters or power converters.
2. Description of the Related Art
FIG. 7 is a plan view showing an example of an internal configuration of a conventional power semiconductor module. FIG. 8 is a circuit diagram relevant to a phase-W circuit of the power semiconductor module of FIG. 7. Here, exemplified is a case of converting unipolar power, which is rectified from AC power, into three-phase AC power (phase-U, phase-V, phase-W).
The power semiconductor module M is provided with frames F1 to F5 made of electrically conductive material on an electrically insulating substrate. The frames F1 and F5 are fed with external unipolar power. For example, a terminal P of the frame F1 is connected with a positive line of an AC power rectifying circuit, while a terminal N of the frame F5 is connected with a negative line of the AC power rectifying circuit.
A terminal W of the frame F2 outputs the phase-W of AC power to an external circuit. A terminal V of the frame F3 outputs the phase-V of AC power to an external circuit. A terminal U of the frame F4 outputs the phase-U of AC power to an external circuit.
On the frame F1, mounted are switching devices S4 to S6, such as IGBT (Insulated Gate Bipolar Transistor), and flywheel diodes D4 to D6. The collectors of the switching devices S4 to S6 and the cathodes of the diodes D4 to D6 are electrically connected to the frame F1.
The emitter of the switching device S4 and the anode of the diode D4 are connected to each other using a short connecting wire, and also to the frame F4 using a relatively longer connecting wire L4. Likewise, the emitter of the switching device S5 and the anode of the diode D5 are connected to each other using a short connecting wire, and also to the frame F3 using a relatively longer connecting wire L5. Further, the emitter of the switching device S6 and the anode of the diode D6 are connected to each other using a short connecting wire, and also to the frame F2 using a relatively longer connecting wire L6.
Meanwhile, on the frame F2, mounted are a switching device S3, such as IGBT, and a flywheel diodes D3. The collector of the switching device S3 and the cathode of the diode D3 are electrically connected to the frame F2. The emitter of the switching device S3 and the anode of the diode D3 are connected to each other using a short connecting wire, and also to the frame F5 using a relatively longer connecting wire L3.
On the frame F3, mounted are a switching device S2, such as IGBT, and a flywheel diodes D2. The collector of the switching device S2 and the cathode of the diode D2 are electrically connected to the frame F3. The emitter of the switching device S2 and the anode of the diode D2 are connected to each other using a short connecting wire, and also to the frame F5 using a relatively longer connecting wire L2.
On the frame F4, mounted are a switching device S1, such as IGBT, and a flywheel diodes D1. The collector of the switching device S1 and the cathode of the diode D1 are electrically connected to the frame F4. The emitter of the switching device S1 and the anode of the diode D1 are connected to each other using a short connecting wire, and also to the frame F5 using a relatively longer connecting wire L1.
Incidentally, for avoiding complexity of the drawing, illustration of the respective gate of the respective IGBT and the respective wire connected with each gate is omitted.
In this configuration, the switching devices S6 and S3 are series-connected between the frames F1 and F5, which are fed with unipolar power, to control the phase-W of AC power. The switching devices S5 and S2 are series-connected to control the phase-V of AC power. The switching devices S4 and S1 are series-connected to control the phase-U of AC power.
A snubber circuit for suppressing surge voltage which may occur in the outputted AC power, is externally connected to the power semiconductor module M. The snubber circuit is typically composed of capacitor, diode, resistor, etc.
Referring to the phase-W of AC power, for example, as shown in FIG. 8, a snubber circuit SN1 is connected between the terminals P and W, and a snubber circuit SN2 is connected between the terminals N and W. Alternatively to the snubber circuits SN1 and SN2, another snubber circuit SN3 may be connected between the terminals P and N.
For the other phase-U and phase-V of AC power, the snubber circuits SN1 and SN2, or SN3 are connected like phase-W.
In such an internal configuration of the above-described power semiconductor module M, since the frames and the semiconductor devices are mutually connected using the connecting wires L1 to L6, total length of the wiring path where each of main circuit current flows is likely to be relatively larger. Hence, due to inductance of the wiring path, relatively higher surge voltage easily takes place during switching operation of the switching devices S1 to S6. Such a higher surge voltage may increase switching loss of the switching devices S1 to S6, or cause breakage of the devices.
As shown in FIG. 8, external connection of the snubber circuits SN1 and SN2, or SN3 with the power semiconductor module M can suppress the surge voltage to some level.
However, in a case of the conventional power semiconductor module M having remarkably larger inductances of the connecting wires L1 to L6, it is difficult for the external snubber circuit to sufficiently suppress surge voltage which takes place within the module.
The related prior arts are listed as follows: Japanese Patent Unexamined Publications (kokai) JP-2000-82775 A1, JP-3-136412(1991) A1, JP-8-32021(1996) A1, JP-2004-112999 A1.